This invention relates to optical devices, and, more particularly, to an all-reflective optical de-rotation device that separately processes two beams and tends to negate the effects of bearing imperfections.
In one type of optical system, an optical train directs a beam into a detector. The detector converts the beam energy into electrical signals, which are processed for viewing or analysis. All or some of the optical train may be supported on a gimbal structure to permit it to be pointed at portions of a scene that are of interest. As the gimbal articulates to change the pointing direction, the beam rotates so that the image on the detector rotates.
This rotation of the image is undesirable, as it greatly complicates the image analysis. To overcome this problem, a de-rotation device is included in the optical train. The de-rotation device compensates for the rotation of the beam resulting from articulation of the gimbal. De-rotation devices have typically incorporated a de-rotation segment utilizing prisms and/or planar mirrors and, where the beam is to be imaged, an imaging segment utilizing lenses and mirrors. These conventional devices, while operable, are heavy and complex.
An improved all-reflective re-imaging de-rotation optical device, comprising two planar beam-folding mirrors and an off-axis powered-mirror set, is disclosed in U.S. Pat. No. 5,078,502. The powered-mirror set reimages the beam to form an intermediate image at one of the mirrors, which is the third mirror in the five-mirror embodiment of the '502 patent.
While operable in many applications, the optical device of the '502 patent has some limitations in other applications. Some advanced optical systems utilize and must process two optical beams, each of which requires de-rotation. For example, the two beams may include an imaged, relatively low-energy visible and/or infrared beam that is the image of the scene, and a non-imaged, relatively high-energy near-infrared laser beam that provides ranging, designating, and/or targeting functions. The present inventor has observed that the optical device of the '502 patent is not suitable for processing both of these beams through the same optical train, because the relatively high-energy beam may damage the mirror at which the intermediate reimage is formed.
There is a need for an improved de-rotation optical device which is suitable for processing two different types of beams. The present invention fulfills this need, and further provides related advantages.